"Everything was fine," Soto said. "We gonna be good. They said it's just a little tight, so just going to take a couple days and see how it goes."
Soto, 23, was not in Washington's lineup Monday, but he pinch hit in the eighth and drew a walk.
"He felt good enough to hit, but he couldn't run and we didn't want him to run,'' Nationals manager Dave Martinez said Monday after his team's 3-2 loss in 10 innings. "He got on base for us, and we had to get him out of there.''
The outfielder felt something tighten up behind his left knee and in his calf after making a throw in right field in the top of the third inning Sunday. He exited after running the bases and getting involved in a rundown in the bottom of the fourth.
"It didn't feel that well, so I just take the decision to pull out of the game and make sure everything's fine before I keep going and make it worse," Soto said. "You don't want to go out of the game that easy. I want to be out there, I want to give my 100%, so I wanted to try."
Soto entered Sunday on an eight-game hitting streak. It makes sense for the Nats to be extra cautious with the face of the franchise, whom they are attempting to sign to a long-term contract.
Teammates were worried about Soto before he got the MRI, but he's already showing some progress.
"Today I feel better, and I hope I feel better tomorrow, too, and we take it from there," Soto said. "I'm just going to see how good it is."
Washington opens a three-game series at NL East rival Philadelphia on Tuesday. Right-hander Jackson Tetreault won't pitch against the Phillies after going on the 15-day injured list with a stress fracture in the scapula in his right shoulder.
Tetreault was dealing with some discomfort, then couldn't lift that arm very high after starting Saturday and figured it was time to say something. His MRI showed far worse news than Soto's.
"I would much rather get this fixed than continue to pitch with it and maybe not do well and end up hurting the team," he said. "As much as I want to be out there, this is for the best."
The Associated Press contributed to this report.